05000280/LER-1995-001, :on 950108,Unit 1 Automatic Reactor Trip Occurred Due to Coupling Failed on Main Feed Pump.Cr Operators Acted Promptly & Placed Plant in Safe Hot Shutdown Condition
| ML18153B227 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 02/07/1995 |
| From: | Christian D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 95-047, 95-47, LER-95-001, LER-95-1, NUDOCS 9502140130 | |
| Download: ML18153B227 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(x) |
| 2801995001R00 - NRC Website | |
text
February 4, 1995 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555
Dear Sirs:
10CFR50.73 Virg:inia Electric and Power Company 8mTy Power Station 5570 Hog Island Road Surry, Virginia 23883-0315 Serial No.:
95-047 SPS:BAG Docket No.:
50-2.80 License No.:
DPR-32 Pursuant to Surry Power Station Technical Specifications, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to Surry Power Station Unit 1.
REPORT NUMBER 50-280/95-001-00 This report has been reviewed by the Station Nuclear Safety and Operating Committee and will be forwarded to the Management Safety Review Committee for its review~
Very truly yours, D. A. Christian Station Manager Enclosure cc:
Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 M. W. Branch NRC Senior Resident Inspector Surry Power Station 9502140130 950207 PDR ADOCK 05000280 S
NRCFORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB NO. 3150-0104 (5-92)
EXPIRES 5/31/95 ESTIMATED BURDEN PERRESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSING EVENT REPORT (LER)
COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO (See reverse for required number of digits/characters for each block)
THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503, FACILITY NAME (1)
DOCKET NUMBER (2)
II PAGE(3)
SURRY POWER STATION, Unit 1 05000 - 280 1 OF 6 TITLE (4)
Unit 1 Automatic Reactor Trip Due to CouplinQ Failure on Main Feed Pump EVENT DATE 5\\
LEA NUMBER {6 REPORT DATE {7}
OTHER FACILITIES INVOLVED fB\\
MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NUMBER 05000
- 01 08 95 95
-- 001 00 02 07 95 FACILITY NAME DOCKET NUMBER 05000-OPERATING THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR:(Check one or more) (11)
MODE (9)
N 20.402(b) 20.405(c)
X 50.73(a)(2)(iv) 73.71(c)
POWER 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)
LEVEL (10) 100%
20.405(a)(1)(11) 50.36(c)(2) 50.73(a)(2)(vll)
OTHER 20.405(a)(1)(iil) 50.73(a)(2)(1)
- 50. 73(a) (2) (viil)(A)
(Specify in Abstract below and 20.405(a)(1 )(iv) 50.73(a)(2)(11) 50.73(a)(2)(vlll)(B)
In Text, NRC Form 366A) 20.405(a)(1)(v) 50.73(a)(2)(111) 50.73(a)(2)(x)
LICENSEE CONTACT FOR THIS LEA {12)
NAME I (804r357~3 ~la~~tg Area Code)
D. A. Christian, Station Manaoer COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13}
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TONPRDS TONPRDS B
SL LM N
X BA 65 N
SUPPLEMENTAL REPORT EXPECTED 14)
EXPECTED MONTH DAY YEAR
~ YES NO SUBMISSION DATE (15) 05 31 95 (If yes, complete EXPECTED SUBMISSION DATE)
ABSTRACT (Limit to 1400 spaces, I.e., approximately 15 single-spaced typewritten lines) (16)
Unit 1 was operating at 100% reactor power on January 8, 1995, when Main Feedwater Pump (MFWP) B tripped at 1552 hours0.018 days <br />0.431 hours <br />0.00257 weeks <br />5.90536e-4 months <br /> on low lube oil pressure. A Unit 1 automatic reactor trip from 74% reactor power followed at 1554 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.91297e-4 months <br /> as a result of a Steam Generator (SG) low-low water level signal. All control rods fully inserted. However, insertion of rod K-2 which had a previously existing inoperable individual rod position indicator (IRPI) could not be verified. Prior flux mapping indicated the K-2 Control Rod was operable and capable of oeing tripped. Following reactor trip, the Turbine Driven Auxiliary Feedwater Pump (TDAFWP) started automatically but experienced diverging governor valve oscillations during ramp to full flow and tripped 52 seconds later. The
- MFWP B trip was caused by a failed lube oil pipe coupling. An initial assessment indicated the teflon pipe coupling failed due to over-tightening. IRPI K-2 was repaired and the K-2 Control Rod was verified fully inserted. A root cause evaluation (RCE) of
- the TDAFWP trip determined that the governor valve control system was unstable. The governor was replaced and tested.
Post maintenance test requirements for the TDAFWP governor valve control system will be upgraded to verify stability. When the RCE is finalized, recommendations will be implemented. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv).
NRC FORM 366 (5*92)
J NRCFORM366 (5-92)
U.S. NUCLEAR REGULATORY COMMISSION LICENSING EVENT REPORT (LER)
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FACILITY NAME 111 DOCKET NUMBER 121 SURRY POWER STATION, Unit 1 05000- 280 TEXT (II more space Is required, use addltlonal copies of NRC Form 366A) (17) 1.0 DESCRIPTION OF THE EVENT APPROVED BY 0MB NO. 3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB n14), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.
LER NUMBER 161 PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER 95
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0 2 OF 6 Unit 1 was operating at 100% reactor power on January 8, 1995, when the Main Feedwater Pump (MFWP) [EIIS-SJ,P] B tripped at 1552 hours0.018 days <br />0.431 hours <br />0.00257 weeks <br />5.90536e-4 months <br />.
The operators implemented abnormal procedures (APs), reduced turbine load and reactor power, and started a third condensate pump [EIIS-SD,P] in an effort to restore stable conditions.
The main steam dump valves [EIIS-SB, V] automatically opened as designed to reduce the Taverrref mismatch caused by the operator initiated load reduction. The SG levels initially stabilized, but as the steam dumps modulated to the fully closed position, the SG levels shrank to the low-low level trip setpoint.
At 1554 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.91297e-4 months <br />, Unit 1 experienced an automatic reactor trip from approximately 74%
reactor power due to a SG low-low water level reactor protection system trip signal from SG A. Following the trip, all control rods fully inserted into the core. However, control rod K-2 which had a previously existing inoperable individual rod position indicator (IRPI) [EIIS-AA,21] could not be verified fully inserted. Therefore, shutdown margin calculations were performed assuming the rod had not inserted..
The Reactor Coolant System (RCS) [EIIS-AB] cooled down below the 547°F Tave (no load temperature) and reached a minimum of 528°F. RCS temperature subsequently stabilized at 547°F after closing the Main Steam Trip Valves [EIIS-SB,ISV] and securing the Auxiliary Feedwater Pumps (AFWPs) [EIIS-BA, P]. The reactivity shutdown margin was calculated following the RCS cooldown to verify that Technical Specification and administrative shutdown margin limits were satisfied.
The turbine [EIIS-TA] and generator [EIIS-TB] tripped as designed. The motor driven and turbine driven AFWPs auto started on SG low-low level. During the ramp to full speed, the TDAFWP experienced divergent governor valve oscillations and tripped due to overspeed at 1555 hours0.018 days <br />0.432 hours <br />0.00257 weeks <br />5.916775e-4 months <br />, 52 seconds after it automatically started. The pump was declared inoperable.
The motor driven auxiliary feedwater pumps and MFWP A provided adequate feedwater flow to the steam generators.
At 1855 hours0.0215 days <br />0.515 hours <br />0.00307 weeks <br />7.058275e-4 months <br />, a four hour non-emergency report was made to the Nuclear Regulatory Commission in accordance with 10 CFR 50.72(b)(2)(ii). This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv), automatic actuation of the Reactor Protection System (RPS) [EIIS-JC].
NRC FORM366 (5-92)
U.S. NUCLEAR REGULATORY COMMISSION LICENSING EVENT REPORT (LER)
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FACILITY NAME (1)
DOCKET NUMBER (2)
SURRY POWER STATION, Unit 1 05000- 580 TEXT (If mora space ls required, use additional copies of NRC Form 366A) (17)
2.0 SAFETY CONSEQUENCES AND IMPLICATIONS
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LER NUMBER !61 PAGE 131 YEAR SEQUENTIAL NUMBER REVISION NUMBER 95
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0 3 OF 6 This event resulted in no safety consequences or implications. Appropriate operator actions were taken in accordance with abnormal and emergency operating procedures to ensure the performance of system automatic actions and to respond to abnormal conditions.
On the SG low-low level signal, auxiliary feedwater flow initiated, as designed, and provided flow to the SGs. Following the trip of the TDAFWP, the motor driven pumps continued to run until they were secured at 1602 hours0.0185 days <br />0.445 hours <br />0.00265 weeks <br />6.09561e-4 months <br />. The MFWP A continued to operate during the event. All control rods fully inserted into the core.
However, control rod K-2 which had a previously existing inoperable rod position indicator could not be verified fully inserted. This control rod was assumed to be fully withdrawn from the core for the purposes of the Shutdown Margin calculations performed immediately following the trip.
Prior flux mapping for the K-2 IRPI, conducted pursuant to Technical Specifications (TS) 3.12.E requirements, indicated that this control rod remained operable and capable of being tripped. After the faulty IRPI cable was replaced, the K-2 IRPI indicated that the K-2 Control Rod was fully inserted.
The unit was brought to a stable hot shutdown condition. No conditions adverse to safety resulted from this event and the health and safety of the public were not affected.
3.0 CAUSE
The cause of the reactor trip was the loss of the MFWP B which automatically tripped on low lube oil pressure. The low lube oil pressure was caused by failure of a teflon coupling in the lube oil return line of the inboard motor 1-FW-PM0-182 inboard bearing. An initial assessment indicated that the teflon coupling was deformed due to over-tightening.
Following the reactor trip, Control Rod K-2 could not be verified to be inserted due to a previously failed IRPI. Troubleshooting revealed a faulty IRPI cable located inside Containment.
The TDAFWP started as required on low-low SG level and then tripped. Post trip evaluation indicated diverging oscillations in steam flow to the TDAFWP turbine as the pump ramped to full speed. A Category I Root Cause Evaluation, initiated on January 9, 1995, determined that the oscillations resulted from the TDAFWP governor valve control system. The system was determined to be dynamically unstable. This NRCFORM 366 (5-92)
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FACILITY NAME (1)
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SURRY POWER STATION, Unit 1 05000- 580 TEXT (II more space Is required, use addltional copies of NRC Form 366A) (17)
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LER NUMBER 16)
PAGE (31 YEAR SEQUENTIAL NUMBER REVISION NUMBER 95
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0 4 OF 6 instability caused the oscillations and consequently the TDAFWP to increase in speed to the overspeed trip setpoint. The exact cause of the unstable condition is still under investigation by the root cause team.
4.0 IMMEDIATE CORRECTIVE ACTIONS
Following the trip, Control Room Operators acted promptly to place the plant in a safe hot shutdown condition in accordance with emergency and other operating procedures.
The Shift Technical Advisor calculated the shutdown margin and monitored the critical safety function status trees to verify that the unit conditions were acceptable. Plant response was as expected and the unit was stabilized at hot shutdown.
The Unit 1 TDAFWP was quarantined until the cause of the overspeed trip could be investigated by the ACE Team.
5.0 ADDITIONAL CORRECTIVE ACTIONS
When the main steam dumps automatically opened to admit steam directly to the main condenser, the RCS average temperature (Tave) decreased below 547°F to a minimum of 528°F. The RCS subsequently stabilized at 547°F (no-load temperature).
The RCS cooldown below no-load temperature is expected and has been observed in previous reactor trips.
The cause of this cooldown is well documented and is the subject of a previous ACE.
Corrective actions are being taken as a result of the previous evaluation. The reactivity shutdown margin was calculated following the RGS cooldown to ensure that Technical Specification and administrative shutdown margin limits were satisfied.
The teflon coupling on the MFWP B lube oil return line was replaced and the pump was returned to service.
The remaining lube oil line teflon couplings on Unit 1 and 2 MFWPs were inspected for indications of over-tightening and were replaced, as needed. A Category II ACE was initiated to document the cause of the coupling failure.
A Containment entry was made to troubleshoot the K-2 IRPI.
The investigation revealed a faulty IRPI cable. A spare cable was placed in service and the K-2 IRPI was satisfactorily tested and returned to service. The K-2 IRPI indicated that the Control Rod K-2 was fully inserted.
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FACILITY NAME (1)
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SURRY POWER STATION, Unit 1 05000 - 580 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)
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L.ER NUMBER (6)
PAGE 131 YEAR SEQUENTIAL NUMBER REVISION NUMBER 95
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0 5 OF 6 As a precautionary measure, the Unit 2 TDAFWP was also declared inoperable until further testing and evaluation could verify operability. A 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO was entered to restore the pump to operable status. Testing was completed satisfactorily at 0131 hours0.00152 days <br />0.0364 hours <br />2.166005e-4 weeks <br />4.98455e-5 months <br /> on January 9, 1995. Following an engineering review of the test results, the Unit 2 TDAFWP was declared operable and the LCO was exited at 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br /> on January 9, 1995. A satisfactory cold start test which also tested for governor valve control system instability was performed on January 15, 1995.
A multi-discipline Category I Root Cause Evaluation Team including station and corporate representatives was formed: 1) to identify the cause of the overspeed trip experienced by the TDAFWP; 2) to determine if this overspeed trip was similar to previous overspeed trips; and 3) to identify corrective actions to prevent reoccurrence of the overspeed trip.
The team was supplemented by a representative from the Institute of Nuclear Power Operations (INPO), a consultant, and field service personnel from the turbine and governor vendors.
TDAFWP trips prior to the governor replacement in December 1994 were evaluated and determined not to have the dynamic instabilities experienced during the January 8, 1995 trip. A previous root cause evaluation completed on these TDAFWP trips adequately documents the causes of the trips prior to December 1994. Similarities were observed between the trip on January 8, 1995 and the return to service testing of the TDAFWP in December, 1994.
However, oscillations experienced in December were eliminated by adjustments to the governor valve control system.
Following satisfactory testing (two tests), the TDAFWP was returned to service on December 25, 1994. The TDAFWP was also tested and verified operable on December 27, 1995.
Evaluation and testing by the root cause team determined that the most probable cause of the TDAFWP overspeed trip was unstable characteristics of the installed governor valve control system, including the governor, governor valve and the governor valve linkage. Following extensive investigation of As Found conditions, including additional testing, the governor was replaced and the quarantine was lifted. The governor was sent to the vendor for further testing, disassembly and inspection.
The replacement governor was dynamically tested for instability. Stable operation of the TDAFWP was verified and the pump was declared operable at 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> on January 14, 1995. Four additional cold start tests and one monthly inservice surveillance test on the TDAFWP have been completed satisfactorily since the pump was declared operable.
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FACILITY NAME 111 DOCKET NUMBER 121 SURRY POWER STATION, Unit 1 05000- 580 TEXT (If more space Is required, use addltlonal copies of NRC Form 366A) (17) 6.0 ACTIONS TO PREVENT RECURRENCE APPROVED BY 0MB NO. 3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WliH iHIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB nt4), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.
LER NUMBER 161 PAGE 131 YEAR SEQUENTIAL NUMBER REVISION NUMBER 95
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0 6 OF 6 When the Category II RGE on the MFWP lube oil system teflon coupling is finalized, its recommendations will be implemented.
The testing which was completed following governor replacement to return the TDAFWP to service December 25, 1994, and also during a subsequent test on December 27, 1994, did not detect the instability experienced during the trip on January 8, 1995. As a result of the root cause investigation of the quarantined TDAFWP, post maintenance testing requirements will be upgraded to verify governor stability following maintenance on the governor valve control system.
Recommendations will be implemented when the TDAFWP Category I Root Cause Evaluation is finalized.
Initial results of the Category I RCE were distributed on the INPO Nuclear Network on January 25, 1995. An update will be provided to the network arid a supplemental LER will be issued when the Category I RCE is finalized.
7.0 SIMILAR EVENTS
LER S1-93-002-00 Reactor Trip Due to Low Steam Generator Water Level Coincident with Steam/Feedwater Flow Mismatch Resulting From Main Feedwater Pump Trip 8.0 MANUFACTURER/MODEL NUMBER Manufacturer:
Equipment:
Woodward Governor Company Turbine Driven Auxiliary Feedwater Pump Governor (Model No. PG-PL)
9.0 ADDITIONAL INFORMATION
Unit 2 was operating at 100% reactor power and was not affected by this event. As a precaution, the Unit 2 TDAFWP was declared inoperable until further tests and an engineering evaluation determined the pump to be unaffected by causes that resulted in the Unit 1 TDAFWP failure.